One shot / two shot
One shot / two shot
Colin. Hopefully you have my order for my replacement 'building in ferro' book by now. Meanwhile I have some questions if you wouldn't mind answering please. I remember in your book you stated that you held a preference for 'two shot' plastering. I have recently been speaking to someone who is building in ferro, they advocate 'one shot'. In my mind 'one shot' seems to be a reasonable method due to the lack of one layer of wet plaster having to bond to a dry layer. Can you clarify this for me please? Are there any 'additives' one should consider putting into the mix? Is it in order to place lead ballast into the lower part of the frame work prior to plastering, say in the form of ingots or some such? maybe within a specially constructed frame within the frame............
Hi Barry, One shot mix is certainly the quick way out, and there are many who will argue for it to justify their decision. Experience has shown that the two shot method is far better and much easier in the end. One shot method...... much increased water content causing voids and a high degree of slumping especially in keel area. Greater depth of plaster creates density and chemical changes more noticeable through hull, propogating greater cracking potential at latter stages of curing. Movement of persons within the hull to finish inside causes shape change and damage. Two shot method.....voids between layers are less than in one shot method as bonding agents and proper application minimises them. Plaster cures more evenly. Less time is needed on main plastering day therefore pressures are less and plastering finish is generally better. Voids in keel are virtually eliminated as keel can be vibrated in to a solid area which will be self sealed during the process. Plastering team only needs to tackle outside area of hull, home builder can finish inside at leasure without fear of damaging hull. No additives are used, they are detrimental to the mix. Do not use lead ballast, reasons given in a previous post. regards
Colin. Thanks for answering this subject so promptly. I've been in touch with Carsten Jorgensen, who has built a Fijian, he told me that a cement manufacturer advised him that layers of plaster will 'bond' if applied within 7 days of each other and the hull is cured by 'wetting' for 28 days. Is this to your knowledge, true? Also, I hadn't realised that the ballast was part of the structure, hence the question. Regards.
Hi Barry. There is no time delay problem in bonding the two mixes. The surface of the old is painted as you go with a water soluble bonding agent.